Emulsion type cleaners are employed in the metal treatment industry to clean and passivate a metal surface. These types of cleaners are typically oil based and in the form of a macroemulsion in water. This type of cleaner is typically used to remove gross soil contaminants, fines, and cooling lubricants from machined metal surfaces. The cleaned metal surfaces do not become "water break free" clean in the traditional sense. This type of "cleaner" leaves an oily film on the surface that provides rust protection.
Emulsion cleaners and clean and passivate treatments can sometimes be interchangeable. Emulsion cleaners usually provide longer term passivation. Clean and passivate cleaners are typically employed in applications which require good cleaning and temporary metal passivation. Treated parts may need to remain rust free, while exposed in the manufacturing plant for from several hours up to 30 days. In order to maintain the rust prevention ability, these cleaners are not rinsed. Commercial clean and passivate treatments may be composed of a variety of alkaline builders and surfactants. They also typically contain passivating components, for example: nitrites, amines, and anionic surfactants. Passivation is achieved by formation of a passive iron oxide or barrier film on the metal surface.
Typically, clean and passivate treatments contain low foaming anionic surfactants such as phosphate esters because they are soluble in alkaline solutions. Such surfactants are susceptible to foaming in soft water or deionized (DI) water. Further, they can interact with the soils being removed such as metal working coolants to enhance the foaming. The presence of phosphate in these surfactants gives rise to environmental concerns regarding waste discharge.
In practice, a clean and passivate treatment is exposed to a variety of coolants and lubricants used in machining the metal surface to be treated. Also, a clean and passivate treatment may be employed in different areas where the hardness of the water varies widely. It was discovered that a clean and passivate treatment made up of monoethanolamine and an anionic phosphate ester surfactant (Permatreat 435 available from Betz Laboratories, Inc.), was susceptible to foaming in applications where soft water was used. The foaming problem was most pronounced in systems where Cimtech 400 coolant, a synthetic metal working coolant containing alkanolamine available from Cincinnati Millicron, was employed.